Feature/rails3 prepare for gem release

Following the guidelines in https://www.openproject.org/projects/openproject/wiki/Developing_Plugins, the gem was prepared for release
    
      * added copyright-headers
      * added readme
      * gemspec extended
    
This also fixes an issue with plugins, that want to add views for the my_project_page: The mechanism now looks for blocks in the my_projects_overviews-folder of the plugin and adds them to the configuration using the document's name (Similar to the way my_page does this in core.) An example for this can be found in the documents-plugin, which now provides views that either show all documents the user can see (in my/_documents.html.erb) and scoped to the given project (under my_projects_overviews/_project_documents.html.erb)